A virtual private network (VPN) provides secure communication across one or more shared core networks also referred to as backbones. A VPN service is provided by a Service Provider to a Customer sometimes referred to as an Enterprise. Increasingly Customers are contracting with a Service Provider to manage connectivity between sites. That is, the Customer desires to outsource their inter-site routing to the Service Provider. The Customer sends the Service Provider its routing information, and then relies on the Service Provider to distribute routing information to and from the other sites via one or more VPNs associated with the customer. Accordingly, from the customer's perspective, they may only view their internal routers communicating with their Customer Edge (CE) routers from one site to another through one or more VPNs managed by the Service Provider.
The Service Provider may operate and maintain each customer's inter-site routing connectivity through specific types of VPNs known as Border Gateway Protocol/Multi-protocol Label Switching IP VPNs (BGP/MPLS IP VPNs). These VPNs use the “Border Gateway Protocol” to distribute the routes, and “Multiprotocol Label Switching” to indicate which routes particular packets need to follow. Additional information about BGP/MPLS IP VPNs is articulated in Internet protocol proposal Request for Comment 2547 (RFC 2547) entitled “BGP/MPLS VPN's,” by E. Rosen et al. (and subsequent industry drafts), which has gained acceptance in the industry.
When provisioning VPNs for a customer, the Service Provider configures what is known as its Provider Edge (PE) routers, which are routers that form part of the backbone of the Service Provider. Typically, PE routers connect with one or more CE routers at the customer's sites. A PE router is configured with a VRF table (Virtual Routing and Forwarding table), which is a table that stores routes available to particular sites connected to the PE router.
Route Target attributes are stored in VRF tables and allow a very fine degree of control over the distribution of routes among VRFs. This can be used to create extranets, or to enforce various customer policies. Particular Route Target attributes can be assigned to particular routes. Thus, Route Targets are the mechanisms that enable each PE router to only maintain routing information for the VPNs it is supporting. The use of Import Targets and Exports Targets also provides considerable flexibility in constructing a variety of VPN topologies. More information about Route Targets and encoding may be obtained as part of BGP Extended Communities attributes (see BGP Multi-Protocol Extensions specified in RFC 2848 from the Internet Engineering Task Force).
One area that has become problematic for Service Providers is the management of RT values. As the size and complexity of each customer's routes and polices increase, most Service Providers randomly generate RT values and assign them without further considerations. With larger customers, the quantity of RT values may become exceedingly large making assignment of RT values complicated and prone to errors. One of the challenges, from a Service Provider's perspective, is to effectively manage thousands of customers of varying sizes each potentially having multiple VPNs including a variety of VPN topologies such as bidirectional and/or unidirectional connections between sites. Reducing the amount of information associated with managing each customer's VPNs including RT attributes, can reduce the complexity and efficiency of managing hundreds of thousands of routes and many different customer policies and topologies.